1. Field of the Invention
The present invention relates to a drying apparatus for drying a coating solution applied onto a plate surface of a printing plate and, particularly, relates to a printing plate drying technique preferably adapted to a process of applying a treating solution such as a protective gum solution and succeedingly drying the protective gum solution while carrying a sheet-like printing plate in which a plate surface is rinsed with a rinsing solution after a non-image portion is dissolved and removed with an alkaline treating solution (developer).
2. Description of the Related Art
At the present time, a photosensitive planographic printing plate abbreviated as PS plate is used widely for printing characters, images, etc. For formation of characters, images, etc. on such a photosensitive planographic printing plate, there are known: a method in which a silver-salt photographic film negative plate having an image, or the like, recorded in advance is exposed while brought into contact with a photosensitive surface of the printing plate; and further, a method in which an image is formed by using an electrophotographic technique.
The photosensitive planographic printing plate having an image formed thereon is used as a printing plate after a photosensitive layer in a non-image portion is dissolved and removed with a developer. An example of a treating process thereof will be described with reference to FIGS. 5 to 10.
That is, the sheet-like photosensitive planographic printing plate 1 having an image formed by an electrophotographic technique is carried by rollers in a direction shown by the arrow X. A developing zone A, a rinsing zone B and a gum solution applying zone C are provided along the direction of the carrying of the photosensitive planographic printing plate 1. A drying apparatus D is provided on the downstream side of the gum solution applying zone C.
The developing zone A is provided for applying a developer onto the photosensitive planographic printing plate 1 to dissolve and remove the photosensitive layer of the non-image portion, and it is constituted by two pairs of carrying rollers 2a and 2b, a comb pattern roller 9, spray nozzles 3 for spraying the developer, a developer tank 4, a pump P1 for sucking up the developer stored in the developer tank 4 to thereby supply the pressurized developer to the spray nozzles 3, a piping system 5, a brush roller 40 slidably touching the image surface of the photosensitive planographic printing plate 1 and rotating in a forward direction or in a backward direction, and the like. Incidentally, means for replenishing the developer with a replenishment solution is provided in the developer tank 4.
The rinsing zone B is provided for washing the developer deposited on the photosensitive planographic printing plate 1, and it is constituted by two pairs of carrying rollers 12a and 12b, spray nozzles 13 for spraying a washing solution, a washing solution tank 14, a pump P2 for sucking up the washing solution reserved in the washing solution tank 14 to thereby supply the pressurized washing solution to the spray nozzles 13, a piping system 15, a brush roller 42 slidably touching the image surface of the photosensitive planographic printing plate 1 and rotating in a forward direction or in a backward direction, and the like. Incidentally, means for replenishing the washing solution is provided in the washing solution tank 14.
The gum solution applying zone C which is, provided for applying a gum solution for protecting the printing surface of the photosensitive planographic printing plate 1, is constituted by two pairs of carrying rollers 22a and 22b, spray nozzles 23 for spraying the gum solution, a gum solution tank 24, a pump P3 for sucking up the gum solution reserved in the gum solution tank 24 to thereby supply the pressurized gum solution to the spray nozzles 23, a piping system 25, and the like. Incidentally, means for replenishing the gum solution is provided in the gum solution tank 24.
In the most downstream portion of each of the zones, the photosensitive planographic printing plate 1 is nipped between a pair of rollers so that the solution is prevented from being brought into the next step.
The drying apparatus D which is provided for drying the gum solution applied onto the photosensitive planographic printing plate 1, is substantially designed so that the photosensitive planographic printing plate 1 is dried by warm air while carried by flower pattern comb rollers 6a and 6b. In the drying apparatus D, warm air ducts 31 are provided so as to blow warm air against the upper and lower side surfaces of the photosensitive planographic printing plate 1. As shown in FIGS. 5 and 6, the warm air ducts 31 are formed so that heat generated from a heater 32 is circulated in the warm air ducts 31 by a fan 33. Further, molleton rollers (solution-absorbing rollers) 34a and 34b for wiping off the gum solution are provided on the most downstream side of the drying apparatus D, that is, at an end for discharging the photosensitive planographic printing plate 1.
Incidentally, each of the rollers 2a, 2b, 12a, 12b, 22a and 22b touches the widthwise whole surface of the photosensitive planographic printing plate 1 but, as shown in FIG. 7, each of the flower pattern comb rollers 6a and 6b has a structure which is such that a portion touching the planographic printing plate 1 is minimized as much as possible.
In the developing zone A, the developer is applied onto the photosensitive planographic printing plate 1 having an image formed by an electrophotographic technique, so that the non-image portion is dissolved and removed. Then, the photosensitive planographic printing plate is washed with water in the rinsing zone B. Then, the gum solution for protecting the surface of the printing plate is applied in the gum solution applying zone C.
Next, the printing plate is dried by warm air in the drying apparatus D and then discharged. The following problems have become clear with respect to the application of the gum solution.
Because the gum solution is applied while the photosensitive planographic printing plate 1 is nipped and carried by the two pairs of carrying rollers 22a and 22b, the gum solution ought to be applied uniformly onto the whole surface thereof naturally. According to examination by the inventor of the present application, however, it has become clear that the gum solution is substantially uniformly applied onto the image-forming portion in a range represented by the broken line in FIG. 7 but coating irregularities occur in the peripheral portion outside of the broken line.
Explaining the contents of the coating irregularities more in detail, the quantity of coating on the rear end portion 1b of the photosensitive planographic printing plate 1 becomes larger than the quantity of coating on the front end portion 1a thereof in the carrying direction of the photosensitive planographic printing plate 1 as shown in FIG. 8 and, further, the quantities of coating on the opposite end portions 1c and 1d in the widthwise direction become larger as shown in FIG. 9. Further, the occurrence of coating irregularities on the opposite end portions 1c and 1d may be considered as follows.
That is, there is some case where an aluminum plate, for example, having a thickness of not smaller than 0.1 mm is used as the photosensitive planographic printing plate 1. 0n the other hand, the carrying rollers 22a and 22b are formed from rubber (EPT, silicon rubber, etc.) so as to be soft to the photosensitive planographic printing plate 1. Accordingly, in a state in which the photosensitive planographic printing plate 1 is nipped by the carrying rollers 22a and 22b, it is thought of that gaps g are formed on opposite sides as shown in FIG. 10 and that the gum solution remaining in the gaps g is deposited on the widthwise opposite end portions 1c and 1d of the photosensitive planographic printing plate 1 to thereby bring about coating irregularities.
Although the coating irregularities, state of the photosensitive planographic printing plate 1 and the cause thereof have been elucidated as mentioned above, the photosensitive planographic printing plate 1 is conventionally used upon the assumption that there is no obstacle to its function as a printing plate because substantially uniform coating is performed on the image-forming portion. It has, however, become clear that various problems are caused by the coating irregularities in the case where a drying process following the gum solution applying process is taken into account.
That is, because the coating irregularities is a state in which the gum solution is applied so as to be partially thick, a longer time is required for drying compared with the image-forming portion onto which the gum solution is applied uniformly. On the other hand, each of the molleton rollers 34a and 34b is formed by winding a material having an excellent water-absorbing property and water-holding property, such as sponge, felt, etc., on a metal roller, but there is conventionally a preconception that the molleton rollers had better be kept contactless unless the whole surface of the photosensitive planographic printing plate 1 is dried. Because the drying of the coating irregularities portion lags, the molleton rollers come into contact with the photosensitive planographic printing plate 1 after the running of the photosensitive planographic printing plate 1 to some degree, that is, after increasing the running distance, or increasing heater power to ensure that the molleton rollers 34a and 34b are to be brought into contact with the photosensitive planographic printing plate 1 after the whole surface thereof is dried.
Accordingly, the conventional drying apparatus D is large-sized as the whole and, furthermore, there arise various problems such as that electric power consumption is increased, that a long time is required for the drying process, and the like.